ISRAEL'S INVASION of Lebanon was just one month old on July 4, 1982, when a car carrying four Iranians -- three diplomats and a journalist -- headed toward East Beirut. At a checkpoint run by the Lebanese Forces, an Israeli-backed Christian militia, the Iranians' car was stopped even though it had diplomatic plates and, according to the Iranians, a police escort.

The four Iranians were taken hostage.

Tehran was outraged first by the kidnaping of high-level diplomats and then by the general disinterest in their fate, perhaps remembering the international furor and headlines devoted to the 52 Americans held in Iran between 1979 and 1981. But U.S. mediators and regional governments were all preoccupied with the war, and the four Iranians were virtually forgotten. It turned out to be a costly oversight.

The incident, as recounted by both Iranian and U.S. officials, marked the genesis of the current foreign hostage phenomenon in Lebanon -- a phenomenon that, as Lt. Col. Oliver North's testimony last week made all too clear, became a foreign policy obsession for the Reagan administration. More importantly, the abductions established the precedent and the initial motive for what has since become the most effective terrorism tactic in the Middle East in the 1980s. At least 130 foreigners from 18 nations have been held hostage in Lebanon since 1982.

Kidnaping has become a weapon of choice for terrorist groups for four reasons: Kidnaping is a relatively inexpensive tactic for small, poorly-financed groups to make their presence known. Military and other forms of conventional power that major countries possess are virtually useless against kidnapers. Increased security awareness has made attacks on embassies and government officials as well as hijackings more difficult. The number of targets is almost limitless; they cannot all be defended or protected.

The 1982 incident that started the current wave of kidnapings is almost forgotten now. The four Iranians were never heard from again. Although few knew it at the time, the Christian militia had tripped on a major catch. The only name initially publicized was Mohsen Mousavi, charge d'affaires at Iran's embassy in Muslim-dominated West Beirut. But also in the car was Ahmad Motevasselian. Tehran says he was merely an embassy political officer, but the State Department claims he was a commander of the Iranian Revolutionary Guards who had moved into Lebanon's eastern Bekaa Valley three weeks earlier.

Although the United States paid little attention to the Brian Jenkins is chairman of the political science department at the Rand Corp. and director of research on political violence. Robin Wright, a senior associate at the Carnegie Endowment for International Peace, is a former Middle East correspondent based in Beirut. incident in Beirut, Tehran's theocrats and their Lebanese allies never wrote off the Iranian hostages. In 1985, the United States received word through an independent channel that Iran would help with the half-dozen American hostages who had been seized since the 1982 incident if information was provided about the four Iranians. The United States again checked into the case; word came back that the Iranians were dead. Not attributing much importance to the query, the case again was forgotten.

With the benefit of hindsight, officials in Washington and diplomats who were serving in the Middle East at the time now recognize that the Iranian abductions established a new context and a new model for political violence against the various foreign forces in Lebanon that was later to be widely reenacted.

But in 1982, the United States did not calculate the long-term implications, despite the lessons both sides had learned during the prolonged hostage ordeal at the U.S. Embassy in Tehran. In the meantime, Iran and its Lebanese brethren have pursued and perfected an age-old practice. Political kidnapings were not new to Lebanon. At least 2,000 local Muslims, Christians and Jews have disappeared over the past 12 years of civil strife, according to local relief agencies. Most are believed to have been immediately or eventually murdered, although all factions charge that their rivals still hold hostages.

But since the 1982 incident, the historic pattern of hostage-taking has changed dramatically in both proportions and political repercussions. Governments are now locked in blind struggles with mysterious organizations they can barely identify. Direct communications are non-existent, normal ransom negotiations impossible. And the political consequences of the ensuing crises, unintended by any of the contestants, have gone far beyond the individual lives at stake.

After the 1982 abductions, the groups in Lebanon became more numerous and far murkier. Only in isolated cases have conventional militias been held responsible, such as the Lebanese Forces who allegedly took the Iranians or the predominantly Christian South Lebanese Army, which abducted 21 Finnish United Nations troops for a week in 1985.

Based on information gleaned from freed hostages, the majority of captors appear to be youths who come from poor areas and from communities that have the least political imput. Their leaders are largely unknown. Some are not even groups in the conventional sense, but rather appear to be a constellation of ideologues and thugs often brought together on an ad hoc basis. And a few cells appear to have been formed for a single operation or to have emerged almost accidentally from a family or a neighborhood gang.

A few are leftists, but the most active are the religious extremists, predominantly Shiite Muslims. Islamic politics, which are of neither left nor right, add a new variable to the hostage phenomenon as well as to the world's political spectrum. This new variable has befuddled both the constitutionally-secular United States and the ideologically-atheist Soviet Union.

Another key new component is state sponsorship. Outside powers have deeply confused the issue of responsibility -- and inexorably complicated solutions -- by skillfully exploiting hostage situations to achieve their own ends.

U.S. officials now believe that the intense American reaction to hostage situations actually planted ideas among the captors and their Iranian mentors about the latitude of their demands. In the process, the value of the hostages appreciated -- and, in terms of numbers held, the phenomenon grew out of proportion to any other terrorism tactic.

But the pattern of general violence indicated that the extremists also had a more ambitious goal -- to purge the West from Lebanon and eventually the region. Two specific flashpoints in 1983 -- the U.S.-orchestrated troop-withdrawal agreement between Lebanon and Israel and U.S. warships shelling Muslim militias at the request of the Christian-dominated government -- symbolized what was perceived by a growing number of extremists as Washington's anti-Islamic bias. The tension sparked a reaction.

"The Islamic Jihad organization claims it is responsible for the abductions in order to renew our acceptance of Reagan's challenge and to confirm our commitment," declared the first communique, "that we will not leave any American on Lebanese soil." This power play established the framework for a new variation on international warfare in which the weaker party consistently had the edge.

The role of Iran, which had an ax to grind because of its own "missing" envoys as well as a new ideology to propagate, was pivotal. Between the 1982 kidnapings and the new seizures in 1984, the Islamic republic had stoked the rising passions of religious zealotry in Lebanon. With help from local and imported mullahs, the Revolutionary Guards sent to Lebanon became missionaries more than fighters, drawing on the growing antagonism among Lebanon's Muslim majority toward the West and methodically building up a corps of cells among the faithful.

The tension was first played out in the 1983 bombings of the U.S. Embassy and the Marine and French barracks, during which more than 360 were killed. The Shiites, meanwhile, were rapidly becoming major players in Lebanon.

But by then the Marines were hidden in containers converted into underground bunkers and the temporary U.S. diplomatic quarters were barricaded. That left only civilian targets, such as Malcolm Kerr, president of the American University in Beirut, who was assassinated outside his campus office in January 1984. Although deeply mourned throughout the region, Kerr's death had little political impact.

And, as the extremists quickly learned, the impact and protracted agony of a life hanging in the balance is far more effective than quickly-forgotten murders carried out by an assassin or a suicide bomber. Deaths elicited anger; taking hostages provided leverage. Holding foreigners also guaranteed status, power and attention, all important commodities to extremists from sects that for decades had been ignored or discriminated against. Like buying futures, holding hostages has been, in effect, an investment almost certain to grow in value over time -- as recent events have proven.

In just over three years, Iran and Lebanese groups have elicited unprecedented political concessions directly related to hostage seizures, including millions worth of arms from the United States and an agreement from France to negotiate the release of Iranian funds frozen by Paris since the 1979 revolution; more than $300 million has already been returned.

Even the release of the 766 Lebanese prisoners after the TWA 847 hijacking in 1985 -- the United States' second mass hostage trauma -- was secondary to the captors' broader goals: world recognition that Israel was holding them in violation of international law and public questioning about the price of the U.S. commitment to Israel. And U.S. countermeasures, such as Washington's angry threats or deploying the Sixth Fleet off the Lebanese coast, served only to underscore American impotence in the face of a this new movement; American warships did not impress the young fanatics. No terrorism tactic has ever been so effective.

Other groups with different agendas inevitably began to imitate. In later stages, U.S. officials believe that teams of "professional" kidnapers carried out the abductions on commission from extremist groups or on speculation, hoping later to sell their captives. "Trade" in hostages became lucrative business. Occasionally the two motives overlapped.

A new variable now appears to be further changing the foreign-hostage phenomenon. The turning point was early 1986, when seizures resumed after a lull. Islamic Jihad had stopped abducting foreigners after June 1985, which coincided with the U.S-Iran negotiations. With the exception of the four Soviets picked up by a Sunni group, not a single foreigner was kidnaped by any group in Lebanon for the next six months. And no more Americans were abducted for almost 15 months, until September 1986.

The change is the product of fragmentation, particularly among the various Shiite cells that still fall under the same umbrella. The break-up is similar to the evolution of the Palestine Liberation Organization over the past two decades. At its peak before the 1982 Israeli invasion, the PLO included eight disparate groups. The result in both cases has been even more labyrinthine politics -- and new violence.

The recent proliferation of invisible and untraceable extremist groups has further complicated both prevention of and reaction to hostage-takings. Until last fall, all but one of the U.S. hostages was believed to have been taken by Islamic Jihad. By January 1987, four different groups were involved, at least three of them predominantly Shiite.

But few who know the Middle East or the background to the hostage trend believe that Tehran any longer has total control over the hostages' fate. Release of Kuwait's 17 prisoners, release of Iranian, Lebanese and other prisoners in Europe, return of further Iranian assets held by the U.S. and France, or intervention by others, such as Syria, might end the current hostage crisis. But it will not end the phenomenon.

In light of the new framework established in Lebanon in 1982 and the way the trend has subsequently evolved, hostage-taking is likely to be the most vexing terrorism tactic for the foreseeable future. Hijackings are now more difficult because of increased security. And bombers may be discouraged by fortifications around diplomatic facilities. In comparison with other options, abducting foreign hostages is physically and politically cost-efficient. Last year, the West initiated unprecedented efforts to counter terrorism. The United States bombed Libya, while Washington and most of Europe imposed varied diplomatic and economic sanctions on Syria. Cooperation and intelligence exchanges increased among western allies.

But during the same time period, the United States and other nations with hostages in Lebanon made humiliating concessions. The captors could achieve gains far loftier than ransoms and prisoner releases; they were in a position to shape the foreign policy of major powers.

The greatest danger, however, is that the trend will begin affecting foreign interests in hotspots far beyond the Middle East. In light of the policy response by nations with hostage victims, seizing foreigners almost offers a model for other revolutionary or religious extremist groups. Last Wednesday three Americans and a Briton were taken hostage by Sudanese rebels.

Lebanon's unique chaos has certainly facilitated perpetrators of violence. But any area with a strong foreign presence or influence where central authority is breaking down is also vulnerable. Foreign hostage-taking has now become an "acceptable" norm in the international political arena, a way for outgunned and outmanned Third World countries or opposition movements to challenge powers of both East and West -- and win.